The Malaysian region acted as a land bridge between the Bay of Bengal and the South China Sea, linking mainland Southeast Asia with the rest of the islands. Archaeological data records prehistoric trade before and after the Pleistocene era. During this period coastal prehistoric sites developed into ports of trade and exchange, both intra-regionally as well as with mainland Southeast China. The abundant supply of minerals, such as tin and gold on the Peninsula, led to early settlements, including Hinduized Indonesian settlers, and to extended trading relations. The archaeological stratigraphy of the sites is very complex, with periods of occupation that date from between 200 BC to 10th century AD. Finds at the key sites of Kuala Selinsing and Pulau Kelumpang include semi-precious gemstones, earthenware, jewellery and decorative items, food, and burials, many of which are well preserved due to the oxygen-starving mud in the mangrove swamps.